Filter felts made from poly(m-phenylene isophthalamide) are known in the art and are disclosed, for example, in Forsten U.S. Pat. No. 4,100,323.
It is also known to make fabrics of poly(m-phenylene isophthalamide) by hydraulically entangling staple fibers--see for example, Research Disclosure, 12410, August 1974.
It is also known to process fabrics of poly(m-phenylene isophthalamide) which were made by hydraulically entangling staple fibers by heating the fabric at high pressure with calender rolls--see Research Disclosure, 13002, February 1975.
One widely used commercial design for removing particulate matter (dust) from gas streams utilizes a method which has been designated as the "outside bag" dust collection principle. In this design, dust-containing gas flows into a large compartment containing a plurality of long, substantially cylindrical filter bags, each bag being suspended by its ring-shaped top. A cylindrical wire cage internally supports the bag and prevents collapse of the filter bag when the gas is flowing into it. The dust collects around the outside of the bag, while the cleaned gas flows into and upward through the bag and out the top of the bag into the clean air outflow conduits. The dust collected on the outside surface of the bag is periodically removed by releasing a split-second reverse-flow pulse of compressed air into the top of the bag. The compressed air travels down the length of the bag, causing it to expand. When the pulse of reverse-flow air is stopped, the bag contracts against the cylindrical wire support cage. The expansion and contraction of the bag causes the collected particles to fall off the bag and be collected. The pulses of reverse-flow air cause the bag to "grow" (increase in area of the fabric) over a number of cycles. The contraction against the cage causes the bag to abrade, and the abrasion becomes more severe as the bag grows. The pulse of reverse-flow air is usually applied to one bag at a time in sequence so that the main flow of dust-containing air into the baghouse and clean air flow from it are not interrupted.